With the increasing use of plastic design methods in structural engineering, it becomes necessary to obtain a better understanding of the effect of partial cross-sectional yielding on the flexural-torsional buckling behavior of laterally braced beams. The equations needed to study the buckling behavior of partially yielded beams and frames have been developed. These equations have been used to investigate the strengthening effect of lateral bracing on the buckling capacity of simply supported rectangular beams subject to the following loading conditions: pure moment; concentrated load at midspan; and concentrated loads at the third points of the beam.